488 CTBWOMYS AND PETROMYS CHAP. example of 120 mm. The tail too Is reduced, being in the same example only 42 mm. in length. As in the last two genera the large intestine is about one half of the length of the small intestine. The " Tuco-tuco," genus Ctenomys, has also short ears and tail. The claws of the fore-feet are longer than those of the hind-feet. A related form is Aconaemys (better known as ScMzodon), with similar external characters; it inhabits high localities on the Andes. Petromys is the only genus of the sub-family which is not American in habitat. It is an African form and there is but one species. Its anatomy conforms to that of the genera already considered. The main difference in structure is shown by the teeth. Their surface is uneven, and differs from that of other Hystricomorphs " in that the enamel to the inside of each upper jaw - tooth and outside on each lower jaw - tooth forms two tubercles, to which correspond grooves in the reverse position of the applied teeth." Sub - Fam. 2. laoncherinae. — The genus Echinomys with thirteen species belongs to the Neotropical region. The members of the genus are entitled " Spiny Rats " since they have spines mixed with the fur. The tail is long and the ears are very well developed. Both feet are five-toed. The tail is scaly as well as haired. Trichomys (also called JSTelomys) is very close to the above, and is also from the same part of the world. The genus Cannabateomys contains but one species, C. amblyonyx, which was formerly included in the genus Dactylomys, but has lately been separated by Dr. Jentink.1 The animal is Brazilian and has a total length of 520 mm.,, of which 320 mm. belong to the tail. It is a climbing rat, and in accordance with that way of life has undergone some modifications. The fore- feet are four-toed, the two middle toes being markedly longer than the outer ones. The hind-feet are five-toed with the same greater development of the two middle toes. The claws are small and somewhat nail-like. Dactylomys, also" Brazilian, and with but one species, JD. dactyUnus, differs from the last in the fact that the molars are simpler in form; they are divided into two lobes, each of which 1 Notes Leyd. Mus. 1891. u. 105.